Adjustable seat for railway carriages and the like

ABSTRACT

An adjustable seat adapted particularly for railway carriages and the like, comprising seat and seat-back combination having a dual connection to a fixed base structure, including, on one hand, towards the front and under the seat a sliding and swivelling connection of slideblock and slideguide and, on the other hand, towards the bottom and at the back of the seat-back a connection with tie-rods pivoting between a transverse spindle of the base structure and a transverse spindle of the seat and seatback structure, further including an elastic member such as an extensible rubber cord, exerting a tractive force between the front of the seat-back structure and the back of the fixed base structure, the dimensions and proportions of the seat and of the elastic member providing for an equilibrium balance of the seat in all of its adjusted positions.

United States Patent 1 Danton 1 Jan. 21, 1975 1 ADJUSTABLE sEAT FORRAILWAY cARRlAoEs AND THE LIKE [75] inventor: Jean Louis Danton,Boulogne,

France [73] Assignee: Etablissements Compin, Paris,

France 221 Filed: Mar. 30, 1973 211 Appl. No.: 347,448

Related US. Application Data [30] Foreign Application Priority Data Apr.27, 1970 France 70.15357 [52] US. Cl. 297/329, 297/344 [51] Int. Cl.A471: 1/02 [58] Field of Search 297/300, 302, 310, 317,

3,170,728 2/1965 Barenyi 248/395 X 3,305,264 2/1967 Gunn t t A 297/3463,572,818 3/1971 Lohr u 297/317 X 3,603,638 9/1971 McGregor et a1.248/429 X FOREIGN PATENTS OR APPLlCATlONS 1,270,662 0/1961 France H297/346 Primary ExaminerRoy D. Frazier Assistant Examiner-William E.Lyddane Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [57]ABSTRACT An adjustable seat adapted particularly for railway carriagesand the like, comprising seat and seat-back combination having a dualconnection to a fixed base structure, including, on one hand, towardsthe front and under the seat a sliding and swivelling connection ofslideblock and slideguide and, on the other hand, towards the bottom andat the back of the seat-back a connection with tie-rods pivoting betweena transverse spindle of the base structure and a transverse spindle ofthe seat and seat-back structure, further including an elastic membersuch as an extensible rubber cord, exerting a tractive force between thefront of the seatback structure and the back of the fixed basestructure, the dimensions and proportions of the seat and of the elasticmember providing for an equilibrium balance of the seat in all of itsadjusted positions 7 Claims, 11 Drawing Figures PATENIEU JANZ I IQYSSHEET 1 OF B PATENTEDJANZI I975 SHEET t [If 8 FATENTEB MHZ] i975 SHEET70F 8 PATENTED JANE] I975 SHEET 8 0F 8 ADJUSTABLE SEAT FOR RAILWAYCARRIAGES AND THE LIKE FIELD OF THE INVENTION The present application isa continuation-in-part Application of Ser. No. 113,907; filed Feb. 9,1971, now abandoned.

The present invention relates to an adjustable seat, particularlyadapted for use in railroad cars. More particularly, the inventionrelates to a seat which may readily be adjusted by tipping aseat-and-back assembly of the seat in conformance with the dual movementof a slot which is formed beneath the front of the seat and of a tie-rodfastened at the rear of the seat back.

DISCUSSION OF THE PRIOR ART Tippable seats of generally this type havebeen described, in particular in French Pat. No. 823,912 with thepurpose of reducing the frontage occupied by the seat, in effect, duringadjustment, the top of the seat back moved almost vertically withoutdisturbing any passenger who was seated behind that particular seat.However, such prior art seats were of comparatively heavy construction,considering the state of the art at that time, and during adjustment,with the seat being unlocked, the frictional forces were sufficient toprevent any involuntary tipping over. However, pursuant to present-daytechnological developments, seats are now made of considerably lighterconstruction and, upon the seat being unlocked, there is evolved therisk of its rapidly and inadvertently tipping in one or anotherdirection depending upon the position and weight of its occupant, suchas a child, or possibly a heavy adult.

SUMMARY OF THE INVENTION It is, accordingly, an object of the presentinvention to eliminate the drawbacks encountered in prior art adjustableseats, and to thereby eliminate any risks to any occupant during theadjustment of the seat.

A more particular object of the present invention lies in the provisionof a seat which may be adjusted by tipping the entire seat-and-backassembly, thereby permitting a neutral or quasi-neutral balanceequilibrium to be obtained for the wholeseat-and-back-assemblyandoccupant combination irrespective of the weightof the occupant and of the adjusted position of the seat.

The invention is essentially predicated on the applicants determinationthat, by appropriately designing the dual front-slot and rear tie-rodconnecting structure, a curve is obtained for the path of the center ofgravity of the adjustable seat-and-occupant combination which at firstis almost horizontal and then extends slightly downwardly, but at aslower rate of traverse. Furthermore, this path of the center of gravitymay be effectively compensated for by the extension curve of an elasticmeans, such as a rubber cord, which is under initial tension acting as atractive force between the seat front and the rear of its basestructure.

Consequently the present invention eliminates the need for complex andexpensive seat locking devices which are frequently required in order tomaintain the adjustable seat in a particular adjusted position.

Accordingly, the adjustable seat, which is particularly applicable foruse in railroad cars, comprises a one-piece seat-and-back constructionwhich incorporates a dual connection to a fixed base structure of theseat. The connection includes, first, a forwardly and beneath the seatlocated swivable slideway connection formed by a slideblock and sliderguide and, secondly a downwardly and behind the seat-back connectionprovided through tie-rods swivably supported between a transversespindle of the base structure and a transverse spindle of theseat-and-back structure, with the connections according to the inventioncomprising firstly an elastic member, such as a rubber cord, exerting atractive pull between the front of the said seatand-back structure andthe rear of the fixed base structure and, secondly, predetermining thesize and proportions of the seat and of the elastic means so as toassure the neutral equilibrium of the seat irrespective of its adjustedposition or occupancy.

According to another embodiment of the invention, the elastic meansoperates by exerting a tractive force between, firstly, the front of theseat-and-back structure and, secondly, downwardly and behind the seatback, and with at least one lengthwise extension of the tie rods of theswivable tie-rod connection extending toward the transverse spindle ofthe base structure opposite the seat-and-back structure.

However, this arrangement when utilized in cars in which dining svice isprovided, is generally subject to the problem when the passenger sitsupright, he is of necessity in the far back position of the seatwhereby, when the seat is adjusted into a forward position, thepassenger is reclining too far back for comfortable dining.

Accordingly, a further object of the invention is to provide a seatstructure which permits the passenger to assume a positionsimultaneously upright and forwardly, suitable for dining requirements.

Consequently, according to a further feature of the invention, theadjustable seat is provided with, in addition to the slideblock andslider guide connection, at least one tie-rod connection which ispivotally mounted first at one end on a spindle integrally fastened tothe seat back, and secondly at the other end on a movable slide locatedadjacent a ramp integrally fastened to the fixed seat base structure,including an elastic means, such as a spring, exerting a tractive forcebetween the front of the seat-andback structure and an extension of thetie rod located toward the slide opposite the tie rod, and with theslide being able to assume, alongside the ramp, at least two regulatedstationary positions, in effect, a far-back position and a forwardposition, pertaining which the predetermined size and proportions of theseat and of the elastic means assure their neutral equilibrium withrespect to any seat-and-back-assembly-and-occupant combinationirrespective of the adjusted positions of the combination.

It is important to note that an object of the invention lies in providigmaximum comfort for the passenger, while allowing him to adjust theposition of his seat as desired without each time having to operate alocking device. Further, there are no longer problems as to anyarrangements providing for a straight forward and simple translatorymovement, such as those facilitating adjustment of a driver's withrespect to a steering column of an automobile responsive to the driver'ssize.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the inventionwill now be described in greater detail, in conjunction with theaccompanying drawings, in which:

FIGS. 1 and 2 illustrate diagrammatically in side elevation anadjustable seat according to the invention, with the seat being shown inan upright position in FIG. I and in a rearwardly inclined position inFIG. 2;

FIG. 3 is a partly schematic detail drawing, on an enlarged scale, ofthe central portion of FIGS. 1 and 2, showing through five equidistantrepresentative positions, the positions of the various members and ofthe center of gravity during the adjustment cycle of the seat;

FIG. 4 is a curve showing the tractive force developed by the rubbercord for the five positions of FIG.

FIG. 5 illustrates diagrammatically in side elevation, a seat withattachment of the elastic means onto an extension of one of the tie rodsof the pivotable tie-rod connection;

FIG. 6 is a diagrammatic side elevation of a seat permitting an occupantto assume a position both upright and at full length;

FIG. 7 is a diagrammatic cross-sectional view of the ramp housing theslide associated with a guide which is adapted to lock the slide; and

FIGS. 8, 9, l and 11 are diagrammatic elevational side views of the seatof FIG. 6, illustrating different relative positions of theseat-and-back unit for each of two adjusted positions of the seat.

DETAILED DESCRIPTION Referring now to FIG. 1, which shows the seat inits upright position pursuant to the invention, the seat includes a basestructure 1 supporting on its front portion a fixed pin 2 around which amovable slideblock 3 is adapted to rotate. On its rear portion, there issupported a pin 4 on which there is adapted to turn a tierod linkagewhich is connected to the seat-back by a pin 6. The fixedcushion-and-back unit comprises a double eushion-and-back framework 7supporting an elastic sheet on its forward end. This sheet acts as asupport for the resilient portion of the upholstery 8, there impartingto the seat a suitable configuration for satisfactory passenger comfort.The cushion-and-back framework 7 supports toward its front a guide 9wherein the shoe 3 of the base structure 1 may slide between a rear stop11 and a front stop 12 for effective travel within guide 9. An elasticmeans, formed of a rubber cord I4, is attached, on the one hand, to thefront of the frame 7 by a hook l5 hooked into a suitable housing 16 and,on the other hand, to the rear of the base structure I by means of ahook 17.

In FIG. 1 the guide 9 is pushed back until the front stop 12 buttsagainst the slideblock 3 of the base structure l and the tie-rod linkage5 projects straight up, thereby positioning the pin 6 in its topmostposition, in effect, the seat pad is thus pushed back and the seatbackstraightened up to its maximum extent.

When the occupant desires to adjust the seat from the upright to theextended or rearward position, he moves the cushion forward, causingslideblock 3 to slide in guide 9, with the tie-rod linkage 5 thenretaining the seat-back so that the top thereof moves appreciably in thevertical plane and increasing the inclination of the back relative tothe vertical axis. This extended position, illustrated in FIG. 2, inwhich the seat components are designated with the same referencenumerals, affords the occupant better support in the lumbar region andtherefore imparts him a feeling of ease and comfort.

In adjusting from an upright (as in FIG. I) to an extended position (asin FIG. 2}, the center of gravity of the seat and its occupant isslightly lowered, imparting a somewhat greater ease of seat manipulationin one direction than in the other, however, as previously stated, theinvention provides neutral equilibrium in each of these positions and inthe intermediate positions through an elastic means which is describedin further detail hereinbelow,

Referring now to FIG. 3, which is an enlarged scale detail drawing; fiveequidistant representative adjusted positions of the seat areillustrated, and identified by the designations 0 (extended), b, c. d. r(upright) for each member; pin 2 in guide 9, hook I5 of the rubber cord14, and pin 6 of the tie-rod linkage 5. FIG. 3 also illustrates the fivecorresponding positions of the center of gravity G of theseat-and-occupant combination. It is noted that in FIG. 3, as anonlimitative example, the size and positions of the slide slot 9 andtie-rod linkage 5, restrict the extend of swivel of the latter betweenapproximately l0 in front of the vertical (upright position r) andapproximately 30 in front of the vertical (extended position a); wherebythe path of the center of gravity G is, as previously stated, at firstalmost horizontal (starting fron Gr) then curved slightly downwardly (onarriving at Ga), while the intervals between successive adjusted seatpositions successively decrease (interval GrGd is larger than thosefollowing, and par ticularly larger than the final interval GhGa).During this movement the rubber cord 14 is extended or stretched (fromlSr to having reference to the curve of FIG. 4 showing the lengths L ofthe rubber cord 14 plotted along the x-axis and its tractive effort Falong the y-axis. It becomes apparent that this effort F which, ofcourse, acts in an opposite direction with respect to the lowering of G,increases progressively (due to an initial tension being imparted to therubber cord 14) and uniformly from position r towards position a, so asto exactly correspond to the compensation required by the plotted pathof the center of gravity G (FIG. 3).

It is noted that the arrangements, proportions and contours necessaryfor obtaining such a result are based on an extensive study of thedynamics of the adjustable seat and clearly varies from the known art,the latter of which is directed chiefly into research pertaining totranslatory motion of the seat-and-back for which a locking means isindispensable.

Referring now to FIG. 5; the seat is constructed of a permanent base 31supporting toward its front a fixed pin 32 having pivotably supportedthereon a movable slideblock 33, and supporting at its rear a pin 34 onwhich is pivotably supported a tie-rod linkage 35 which is connected tothe seat-back by a pin 36. This tie-rod linkage is extended beyond thepin 34 by a lever arm 37, the fixed seat-and-back unit being composed ofa double seat-and-back framework 38 supporting an elastic sheet on itsfront portion. The seat-and-back framework 38 supports on its frontportion a guide 39 within which the slideblock 33 of the base 3| mayslide between a rear stop 41 and a front stop 42 limiting the travelwithin guide 39. An elastic means formed of a rubber cord 44 is attachedat one end thereof to the front of the moving frame 38 by a hook 45hooking into a suitable recess 46 and at its other end to a lever arm 37by means ofa hook 47. In the case where the adjustable seat includesseveral tie-rod connections, the cord 44 may also be attached to a stayor cross-bar uniting all of the lever arms which are similar to leverarm 37. The tractive action of the elastic means 44 on the lever arm 37impart to the seat-and-back-and-occupant combination an improved neutralequilibrium, and concurrently facilitates the ready return of the seatto its rear position.

Referring now to FIG. 6, the seat is constructed of a unitaryseat-and-back structure provided with a dual connection to a fixed seatbase, such as, toward the front and beneath the seat, a movableslideblock and guide connection including a mobile slideblock 51pivotably supported on a fixed pin 53 mounted on the base 54, and of aguide 55 wherein the slideblock 51 is adapted to slide in a travel pathlimited by a front stop 56 and a rear stop 57.

A second connection includes a tie rod 58 which is 'pivotably mounted,on the one hand, about a pin 59 integrally formed with the seat-back 60and, on the other hand, on a pin 6! located on a slide 62 which ismovable along a ramp 63 integrally formed with the base 54. Extendingparallel with the ramp 63 and along a side face of the slide 62, a guide64 is attached thereto, and on which a skid 65 is supported while fittedon the top end of an arm 66 of a first-class lever 67. The lever 67 isbent into a slight V-shape, and pivotally supported at its fulcrum on apin 68 integrally fastened with the base 54. The guide 64 has twogrooves or recesses 69 and 70 in which the skid 65 of the lever arm 66may engage, so as to provide for suitable positioning of the slide 62 onthe ramp 63, and thereby locking the slide 62 into a positioncorresponding to one or the other of grooves 69 and 70. The retention ofthe skid 65 against the guide 64, and its engagement in either of thegrooves 69 or 70 is established by the resultant couple (torsionalforce) generated by a spring pulling between the lever arm 71,homologous to the lever arm 66 and the base 54. it becomes apparent thatsuch a result may be obtained by a torsion spring fitted onto pin 68, orby a compression spring extending between lever arm 66 and the base 54.The disengagement of the skid 65 externally of either one or other ofthe grooves 69 or 70, in which it was previously engaged, may beeffected by simply exerting an upward vertical force, on lever arm 71 inopposition to the previously mentioned resultant couple. In order toprevent the angle of tie rod 58 and seat-back 60 not being able torecover beyond a predetermined limit, an adjustable stop 72 is broughtto bear on a plate 73 attached to tie rod 58.

The elastic means is composed of a spring which exerts a pull betweenthe seafront 74 and an extension 75 of the tie rod 58 located toward theslide 62 opposite the tie rod 58.

The operation of the seat unit is such that for stan dard use thereof,the slide 62 is locked in the rear position, with the skid 65 of leverarm 66 being positioned in groove 69. In this position, partlyillustrated in broken lines in FIG. 6, with the pin for swiveling tierod 58 on slide 63 being in a position illustrated by reference numeral78, the seat acts in the identical manner described in connection withthe seat illustrated in FIG. 5.

In order to reach the dining position. slide 62 is unlatched by actionon the lever arm 71, and is advanced along ramp 63 until the skid 65engages in the groove 70, in consequence of which, the pin rotating thetie rod 58 on slide 62 moves into the fixed position designated byreference numeral 79.

During the course of this movement, since the angle between theseat-back 60 and the tie rod 58 is being decreased, the stop 72 comesinto contact with the plate 73 of tie rod 58 and the seat-and-backassembly is projected forwardly, the guide 55 being moved into a forward position as it slides relative to the slide-block 5|.

A new usable range of adjustment is obtained, whereby the seat may beimparted a more forwardly and horizontal position, and with the backbeing also more forwardly and at the same time vertically straightened.

The inclination of ramp 63 as well as the position of the varioussliding elements of the seat are, of course, so calculated as to attainas comfortable a position for dining as is possible.

Furthermore, the slide 62 may be supplied, in lieu of a guide 64, with arack having teeth which are adapted to mesh with teeth arranged on thelever arm 66 instead of the skid 65. In that instance, the slide 62 mayenter a plurality of fixed positions along ramp 63.

Referring now to FIG. 7, a slide 62 which is of parallelpipedal shape isguided, by its members, along two channel sections 80 and 81 of thesloping ramp 63, by means of associated bearing balls 82 on the twolongitudinal side faces of the slide 62, and on the internal face of thecore of the two channel sections 80 and 8|. The upper surface of thisslide 62 is rigidly connected to the web of a U-section bearing 83 towhich is attached, on the one hand, extending transversely to the twolegs 84 and 85, the pin 86 for swiveling the tie rod 58 and, on theother hand, to the outer surface of the leg 85, a metal angle iron 87.This metal angle iron carries the channel guide 64. The web of thisguide, as well as the corresponding portion of angle iron 87, comprisesthe two grooves 69 and utilized for locking the slide 62.

In order to avoid any error in interpreting the description, normalservive positions of the seat refers to all positions of the seatobtained for the far-back position of the slide 62 along the ramp 63,and dining (or meal) positions" all positions of the seat obtained forthe forward position of the slide 62 along ramp 63.

FIG. 8 is a diagrammatic section of a seat similar to that of FIG. 6,illustrating two relative positions of the seat, namely, in solid linedesignated by reference numeral 88, a normal service position in whichthe seat is pushed back and the back is straight up, and in broken linedesignated by reference numeral 89, another normal position in which theseat is moved forward and the back is inclined.

Similarly, FIG. 9 illustrates in solid line, through reference numeral90, a seat in normal service position according to which the seat ispushed back and the back straight up, and in broken line throughreference numeral 91, a dining position according to which the seat ismoved forward and the back slightly inclined.

The two positions shown in solid lines in FlGS. l0 and 11 throughreference numeral 92, correspond to a dining position in which the seatis pushed back and the back is straight up.

The position shown in broken line in FIG. 10 through reference numeral93, is a normal service position similar to that shown in full line inFIG. 2 by reference numeral 88.

Finally, the position shown in broken line in FIG. 11 through referencenumeral 94, is a dining position similar to that shown in broken line inFIG. 9 by reference numeral 91.

While there has been shown what is considered to be the preferredembodiment of the invention, it will be obvious that modifications maybe made which come within the scope of the disclosure of thespecification.

What I claim is:

1. An adjustable seat, particularly for railroad cars and the like,comprising an adjustable unitary seat-andback structure; a fixed base; adual connection between said fixed base and said seat-and-back, a firstof said connections including, toward the front and beneath the seat, aslideway fastened to said seat-and-back structure so as to be movabletherewith, said slideway having a slideblock and a slider guide slidablymounting said slideblock, a fixed pin fastened to said base, saidslideblock being rotatably connected to said pin; the other of saidconnections including, downwardly and behind the seat-back, atransversely extending pin on said base and a transversely extending pinon said seatand-back structure, a tie rod linkage swivably sup portedbetween said pin on said base and said pin on said seat-and-baekstructure facilitating tilting of said seat-and-back structure relativeto said base; an elastic member connected between the front of saidseat-andback structure and the rear ofsaid fixed base and exerting atractive force therebetween, said seat and said elastic member beingsized and proportioned so as to ensure a neutral equilibrium to aseat-and-back-and' occupant combination in any adjusted position of saidseat; and means limiting travel of said tie-rod linkage between saidfixed base and said seat to between two positions of said tie-rodlinkage forwardly of a vertical axis.

2. A seat as claimed in claim I, said elastic member comprising a rubbercord.

3. A seat as claimed in claim 1, said means limiting travel of saidtie-rod linkage to between said two positions of said tie-rod linkage inthe range of about l0 to forwardly of said vertical axis, said elasticmember exerting said force with an initial tension between a point ofthe seat proximate to and above said slider guide and a point on saidfixed base structure proximate to and below said transverse pin on saidfixed base, the tractive force of the elastic member acting in adirection opposed to a lowering of the center of gravity of theseat-and-back-and-occupant combination, and said force increasingprogressively and uniformly in response to an initial tension impartedto said elastic member at a progressively lower increase from astraight-up seat position toward an extended seat position so as toprovide corresponding compensation for the path of movement of saidcenter of gravity. thereby imparting neutral equilibrium to theseat-and-backand-occupant combination.

4. A seat as claimed in claim I, said elastic member exerting a forcebetween the front of said seat-andback structure and the back of theseat; and at least one longitudinal extension of the tie rod linkagebeing located so as to extend toward said transverse pin on saidseat-and-back structure.

5. A seat as claimed in claim 1, comprising at least one further tie-rodlinkage connection pivotably mounted at a first end thereof on one endofa pin integrally fastened to the seat back, and at its other end, to aslide movable along a ramp integrally fastened to said fixed base, saidelastic member exerting a pull between the front of said seat-and-backstructure and an extension on said further tie rod linkage, and beinglocated toward said slide opposite said tie rod linkage, said slideadapted to be moved along said ramp into at least two regulatable fixedpositions defining, respectively, a farback seat position and a forwardseat position, the size and proportions of the seat and of said elasticmember ensuring neutral equilibrium of the seat-and-back-andoccupantcombination, irrespective of the postions of said combination.

6. A seat as claimed in claim 5, comprising locking means for said slideincluding a guide attached to a side face of said slide and extendingparallel to said ramp, at skid supporting said guide, said skid beingmounted on the top end of an arm of a V-shaped lever; a spindleintegrally fastened to said fixed base, said lever being fulcrumed onsaid spindle, said guide having two stepped grooves adapted to have saidskid engaged therein so as to lock said slide into a positioncorresponding to one or the other of said grooves; and spring meansretaining the skid against the guide and in engagement in one of saidgrooves in response to a resultant torque force generated by the actionof said spring means.

7. A seat as claimed in claim 6, said guide comprising a toothed rack;said lever having teeth on at least one arm thereof adapted tointerdigitate with said toothed rack.

1. An adjustable seat, particularly for railroad cars and the like,comprising an adjustable unitary seat-and-back structure; a fixed base;a dual connection between said fixed base and said seat-and-back, afirst of said connections including, toward the front and beneath theseat, a slideway fastened to said seat-andback structure so as to bemovable therewith, said slideway having a slideblock and a slider guideslidably mounting said slideblock, a fixed pin fastened to said base,said slideblock being rotatably connected to said pin; the other of saidconnections including, downwardly and behind the seat-back, atransversely extending pin on said base and a transversely extending pinon said seat-and-back structure, a tie rod linkage swivably supportedbetween said pin on said base and said pin on said seat-and-backstructure facilitating tilting of said seatand-back structure relativeto said base; an elastic member connected between the front of saidseat-and-back structure and the rear of said fixed base and exerting atractive force therebetween, said seat and said elastic member beingsized and proportioned so as to ensure a neutral equilibrium to aseat-andback-and-occupant combination in any adjusted position of saidseat; and means limiting travel of said tie-rod linkage between saidfixed base aNd said seat to between two positions of said tie-rodlinkage forwardly of a vertical axis.
 2. A seat as claimed in claim 1,said elastic member comprising a rubber cord.
 3. A seat as claimed inclaim 1, said means limiting travel of said tie-rod linkage to betweensaid two positions of said tie-rod linkage in the range of about 10* to30* forwardly of said vertical axis, said elastic member exerting saidforce with an initial tension between a point of the seat proximate toand above said slider guide and a point on said fixed base structureproximate to and below said transverse pin on said fixed base, thetractive force of the elastic member acting in a direction opposed to alowering of the center of gravity of the seat-and-back-and-occupantcombination, and said force increasing progressively and uniformly inresponse to an initial tension imparted to said elastic member at aprogressively lower increase from a straight-up seat position toward anextended seat position so as to provide corresponding compensation forthe path of movement of said center of gravity, thereby impartingneutral equilibrium to the seat-and-back-and-occupant combination.
 4. Aseat as claimed in claim 1, said elastic member exerting a force betweenthe front of said seat-and-back structure and the back of the seat; andat least one longitudinal extension of the tie rod linkage being locatedso as to extend toward said transverse pin on said seat-and-backstructure.
 5. A seat as claimed in claim 1, comprising at least onefurther tie-rod linkage connection pivotably mounted at a first endthereof on one end of a pin integrally fastened to the seat back, and atits other end, to a slide movable along a ramp integrally fastened tosaid fixed base, said elastic member exerting a pull between the frontof said seat-and-back structure and an extension on said further tie rodlinkage, and being located toward said slide opposite said tie rodlinkage, said slide adapted to be moved along said ramp into at leasttwo regulatable fixed positions defining, respectively, a far-back seatposition and a forward seat position, the size and proportions of theseat and of said elastic member ensuring neutral equilibrium of theseat-and-back-and-occupant combination, irrespective of the postions ofsaid combination.
 6. A seat as claimed in claim 5, comprising lockingmeans for said slide including a guide attached to a side face of saidslide and extending parallel to said ramp, a skid supporting said guide,said skid being mounted on the top end of an arm of a V-shaped lever; aspindle integrally fastened to said fixed base, said lever beingfulcrumed on said spindle, said guide having two stepped grooves adaptedto have said skid engaged therein so as to lock said slide into aposition corresponding to one or the other of said grooves; and springmeans retaining the skid against the guide and in engagement in one ofsaid grooves in response to a resultant torque force generated by theaction of said spring means.
 7. A seat as claimed in claim 6, said guidecomprising a toothed rack; said lever having teeth on at least one armthereof adapted to interdigitate with said toothed rack.